Means for and method of amplitude selection



Jan. 22 1924.

R. W. DEARDORFF MEANS FOR AND METHOD OF AMPLITUDE SELECTION Filed Oct, 5, 1921 3 Sheets-Sheet 1 I v NVENT ATTORNEY Jan." 22 1924. 7 12,483,284

R. w. DEARDORFF MEANS FOR AND METHOD OF AMPLITUDE SELECTION Filed Oct. 5,1921 3 Sheets-Sheet 2 Psz/Jtant [/1 01/5 0026 K ill Q3 arahzlf L 6 ATTORNEY R. W. DEARDORFF MEANS FOR AND METHOD OF AMPLITUDE SELECTION Jan. 22, 1924.

' s Sheets-She et 5 Filed 061;. 5, 1921 NVENTOR ATTORNEY Patented Jan. 22, 15 324.

UNITED STATES, PATENT, OFFICE.

aura w. Dmnonrr, or BROOKLYN, new YORK, nssmuos. 'ro mnmcm TELE PHONE AND TELEGRAPH COMPANY, A CORI'QRATION OF NEW YORK.

mums Fo'a mn'rnon or AMPLITUDE SELECTION.

' Application filed ctober""5, 1921;. Serial No. 5053591.

To all whom it may concern Be it known that I, RALPH \V. DEannonFF, Y

residing at Brooklyn, in the county of Kings and State of New York,.have invented cere tain Improvements in Means for and Methods of Amplitude Selection, of which the following is a specification.

This invention relates to the art of signaL' ing and more particularly to multiplex signaling. i r In its broader aspects the invention relates to methods of and means for selecting be- In the selection of any given signaling current from a number of superposed sig naling currents, it has long been known that, if the various signaling currents have characteristic frequencies, a simple method of discrimination is at once available. -\Vl1e re.

:m however, the distinctive characteristic of the everal signaling currents is one of am- )litude, the problem is not so readily solved. he three-element vacuum tube, however,

a has certain characteristics which render it- :25. available as an lnstrumeuta'hty for amphtude discrimination. 'In accordance with the present invention therefore, it is proposed to usecertaincombinations of vacuum tubes and circuits wherebv thc signaling currents of a given amplitude may be selected to the exclusion of any desired number of super posed signaling currents all having different amplitude. p The invention may now be more fully un- 7- derst00d from the following descriptlon,

when read in connection with the acco mpany'ing drawing in which:

Figure 1 1s a diagram of a simple form of vacuum tube circuit adapted to be used in connection with the amplitude selection of slgnahng current;

Flg. 2 is a series of curves illustrating the characteristics of the vacuum tube of Fig. 1;

' 3 is a diagram showing one form of vacuum tube selectin circuit for discriminating between signa mg currents of differ ent ampiitudes Fig 4 is aserles of curves illustrating the operation of the arrangement of Fig. 3;

Fig. 5 is a diagram of-a circuit arranged simi lar to that of Fig. 3, but havingcertain mproved features not present in Fig. 3;

' Figs. 6 to 9, inclusive, are curves illustrating thej operation of the arrangement. of

F1 .5; I ig. 10 is acircuit diagram of a vacuum tube amplitude'selecting organization capable of selecting by means of its amplitude charactertistic a given signaling current from 1 any number of superposed'signaling currents; and

"Figs. 11 to 13, inclusive show curves illustrating the operation of the arrangement of i Fig. 10.

Referrlng to Fig. 1 V designates a vacuum tube of the usual t pe, having a filament, grid and plate. T e input circuit includes the usual battery C for determining the grid potential, and the outpu circuit includes the usual battery B for supplying the plate current. A battery A is provided for heating the filament and the current supplied by this battery to the filament may be regulated by means of a resistance 10.

It is a well-known factthatin a circuit arrangement of this kind the maximum cur-' ages to some desired maximum value within the limits of saturation, the temperature of the filament being fixed at such a point as to obtain a sufliciently high saturation.

' Referring'to Fig. 2, for example, 11 designates a curve representing the variation of the plate current with the grid potentlal, the grid potential being plotted horizontally and space current. being plotted vertically. It

will be noted that the space current does not increase after a certain grid potential has been reached, this being indicated by the fiat part of the curve. By lowering the filament temperature, or lowering the plate voltage, this flat part of the curve may be lowered as much as desired.

If now the potential of the C battery be so chosen as to bring the normal potential f the grid to the point indicated by the dotted line 12 in thediagram, and an alternating signal, as indicated by the curve marked signal S, be superposed upon the grid potential, a variation in the space current will occur, as is indicated by the curve S,. If an alternating signal current S of great amplitude be superposed upon the normal grid potential, 3, similar variation in the space current, as indicated by the curve S, will occur, and the maximum amplitude of this variation will be no greater than in the case of the signal S,, owing to the saturation characteristic of the tube.

Referring now to Fig. 3, it will be shown how this principle may be employed in selecting either of two signals of different amplitude. The tube V, in Fig. 3 is adlscriminating tube similar to that shown in Fig. 1, and its grid potential and filament temperature may be regulated, so that its characteristic curve will be similar to that of the curve 11. Signals from a line L, may be impressed upon this tube through a potentiometer 13, the potentiometer determining the amplitude of the variations impressed upon the grid due to the signal. The output circuit of the tube V, may be associated with an outgoing line L, through a transformer 14.

A second tube V of construction similar to that of the tube V, may be connected with the line L, through a potentiometer 15. The filament temperature, plate voltage and the normal rid potential of the tube V may be so adj uste or chosen that the tube will have the usual amplifying characteristic. In general its characteristic curve will be similar to that of the curve 11 of Fig. 2 and the saturation point will be sufliciently high' and the potentiometer-15 so adjusted that for signals of amplitudes S, or S the tube will operate along the straight portion of its characteristic on either side of the dotted line 12. This will result in reproducing in the output circuit of the tube V, in response to signals impressed on the input circuit, current variations similar in both form and relative amplitude to those impressed on the input circuit. The output circuit of the tube V is associated with the line L, through a trans- -former 16 which is so wound that the effect produced in the circuit L, will oppose the" amet s ignalswhen passed through the amplifyin tube V will a pear in the output circult with such amplitudes that the amplitude of one of them, for example, the signal S will be the same in the output of tube V as the amplitude of the corresponding signal when passed through the discriminating tube V,. The amplitude of the other signal (S, in the case assumed) will be less than that of the signal S As a consequence, the signal in the output circuit of the tube V,,, corresponding to S will balance out in the line L, the corresponding component in the output of the tube V,. The two components corresponding to the signal 55,, however, will not balance, and consequently, the signal S, will be received in the line L, and the signal S will be excluded.

If the potentiometers l3 and 15 are given a different relative adjustment, the amplitude of the signal S, in the output circuit of the tube V, may be made just equal to that of the component corresponding to S, in the output circuit of the tube V,. In this case, the components corresponding to the signal S, will balance out in the line L,,, but the amplitude of the signal S appearing in the output circuit of the tube V will be greater than that of the corresponding component in the output circuit of the tube V,,

and the signal S will accordingly be received in the line L It is also possible to utilize a single tube in such a manner as to select a current of greater amplitude to the exclusion of one of lower amplitude by employing a circuit such as that shown in Fig. 1. For example, let us suppose the characteristic of the tube V of Fig. 1 to be as shown at 17 in Fig. 4, and that the C battery be adjusted so that the normal grid potential Will be that indicated by the dotted line 18, this potential being somewhat more negative than the point of the upper knee of the curve If, now, a signal of amplitude S, be superposed upon the grid potential, the signal will be practically suppressed. owing to the fact that the curve at this point is almost flat. The variation in the direct current flowing in the output circuit will be as shown at S,. A signal of greater amplitude, such as S,, will however, result in a rectified current in the output circuit, as indicated by 8,, because in this instance the positive halves of the signal wave bring the grid potential up on the slope of the characteristic curve. The signal variations S, and S when passed through the output transformer, will cause alternating currents corresponding to the curves S," and S to appear in theoutput circuit. It Wlll be noted that the curve S, will, except for a certain amount of distortion. correspond to that of the signal S while the curve S," represents a practically negligible current variation. Accordingly, the

loo

emes signal S," is, for all practical purposes,

suppressed.

1 tubes being connected in a circuit organizacomponent of lesser amplitude tion such as shown in Fig. 3. Inthis case it will befseen'thatonly the sigal S, will be passed through the tube V,. y properly adjusting the otentiometers, the amplitude of the signal S, appearing in the output circuit of the amplifier V,'may be. made equal to the corresponding com onent in .the output circuit :of the tube These two components will accordingly balance out in the line 'L,, but the signal S of small amplitude will not'ubehbalanced out, due to the fact that it was transmitted through the tube V, but not through the tube V The arrangement just described is subject to-the objection that only one half of the signal wave is. transmitted and a certain amount of distortion of the si al wave occurs in the discriminating tu e. These difficulties are overcome by means of. the. modified arrangement shown in Fig.5. Inthis case the discriminating arrangement-if comprises two tubes V, and V, connected in a balanced circuit in such a manner thatwaves of one sign will be rectified input I by the tube V and the input waves of the other sign will be rectified by the tube" V,'. Consequently, both halves of an alternating input signal will be reproduced in the output side of the apparatus, except for the distortion, due to the fact that the tubes. are operated below the knee of the curve.

' The normal grid potential may, of course,

be adjusted as indicated in Fig. 4, so that for'signals of small amplitude, practically I no transmission will take lace through the.

tubes V and V but in t e case or si of greater amplitude, both halves o the 1 may be included between the line L,

the discriminating tubes V and V,'

arranging the upper cut-oil of this filter wave will be transmitted, subject, of course,

to a certain degreeof distortion. In order -to eliminate the harmonics introduced by the distortion, :1 low pass or band filter 19 and By sufficiently high to pass the fundamental -signaling. frequency but to su press harmonies of this frequency the distortion of the signal will be entirely eliminated and the signal will be restored to its normal sine wave form. The amplifying tube V, will, as in the case of Fig. 3, be so'connected as to 'produceupon the line L, efi'ects opposite to those produced by the output transformer of the discriminating device.

the line L,, as indicated in Fig. 9i

4 distorting. tube als This action is aided by the fact that. the

filtermay in addition to suppressing un desired frequencies, be use as a phase shifting device,

The action of this arrangement in dis- 7o criminating I against current of greater amplitude may be understood from the curves shown in Figs. 6 to 9, inclusive. \In Fig. 6, the curves S and S, represent simple sine waves as applied to the input side of 76- the tubes V and V,-.' The wave S is suppressed in the manner already described, but the wave S,, being of greater amplitude, will be transmitted, and if the tubes are properly adjusted,.'will be amplified as in- ,80

dice-ted by the curve S, of Fig. 7, both halves of the wave being transmitted and both being similarly'distorted. The action of the filter 19 upon the curve S, will be I toproduce asim le'sine wave S,", of lesser ll amplitude thant e wave 8,. Fig. 8 shows the wave S, passed by the filter'19 and superposed upon the waves appearing in the output circuit of -he amplifierV, in opposite phase relatiog. In this diagram the 9t curve 6,"? represents thesignal wave S after-"amplification by the amplifier while the curve S,"' is a similar re resenta-- tion of the wave S, after amp ification.

This wave is just equal to, but opposite inflisign, to the wave S," suppliedby the distorter'. As a consequence, signal S, is sup pressed and the wave SJ" will appear in Where it is desired to suppres rent of lower amplitude without distorting the current of greater amplitude only the I I arrangement V, and the filter 19 will be used, the amplifyi portion of the apparatus being omitte 1106 This results in the production of thev wave S,"= as indicated Sin Fig. 7, which corresponds to the signal of greater amplitude. The arrangements thus far described are only capable of selecting signals amplitudes. When it is desired to select any given signal from superposed signals of more than two amplitudes, the principle employed by the apparatus illustrated in 11! Fig- 10 and the curves of Figs. 11 to 13, inclusive, may be employed. In Fig. 10 a discriminating tube arrangement V,-V with a filter 19 in its output circuit, is asso-.

ciated with the outgoing line L, in a mane ner similar to the corresponding apparatus in Fig. 5. An amplifying tube V is also connected to'the line L, in a manner similar to that shown in Fig. 5. The input branches '21 and 22'leading to the discriminating tube l and the amplifying tube, respectively, are connected in this case, however, to a circuit including a filter 20 instead of being connected directly to the line L The filter 20.

is arranged upon the output side of a dis the cur- W of one no amplitude from superposed signals of two tively.

Let us assume that signals of three amplitudes, S S and-S are being received over the line L, and it is. desired to select the. signal' S to the exclusion ofthe signals S and.

S of lesser and greater amplitude, respectubes V,V, are indicated by curves 23 and 24, respectively, of'Fig. l1, and. the C battery is so adjusted that the normal (grid potential will be at the point indicate by the dotted line 25. The result of the operation of these twotubes will. be to suppress the signal S, in theoutput' circuit ofthe tube but to pass two signals S and S, of greater amplitude, .these signals appearing as S and S, in Fig. 1;1.- The filter 2O eliminates the harmonics introduced by the distortion of the tubes, so thaton the output side of the filter 20 the signals S and S, will again appear as pure sine waves having'the form S and 8,, When these waves are impressed upon a: similar. discriminating tube arrangement VJ-V, having the characteristics indica in Fig. 12,:the component .3 is eliminated and a wave 5,", corresponding to the original signal wave S, will be transmitted the harmonics being suppressed by the filter 19.: The same waves,

fwhen impressed upon the amplifying tube V. having theycharacteristics indicated in Fig. 13, will resultin the reproduction in the output circuit of said tube of both signals S and S, as indicated by the curves "8 and 8 The latter of these curves, it will be noted, is of the same form andamplitude as the component S, appearing in the output circuit of the discriminating arrangement. Consequently, the component correspondin to the signals is balanced out in the line L. but a oomponent Sf, corresponding to'the signal 8,. will be transmitted to the line L, and will be received. Thus it will be seen that we have anarrangement' capable of receiving a band of amplitudes while suppreming those on either side of the received band.

If it is desired to suppress signals of all amplitudes except the signal of maximum amplitude 8,. the amplifying tube V, may

be omitted, in vwhich case only the signal indicated by the curve S," of Fig. 12 will be transmitted. .The same result may be obtained, however, by the use of one pair of discriminating tubes and one filter. For ex-' ample. the tubes=V,-V,, together with the filter 20. maybe used and the normal C potential so adjusted that currents of amplitudesS. and S will fall upon the flat part of the characteristic of the twotubes. This may be done by adjusting the, grid potential so that the dotted line 25 will be moved The characteristic curves of theearner.

furtherto the left. This will result in suppressing signals S and S while the signal 3 will be passed.

If it is desired to transmit to L only the signal of lowest amplitude such as 8,, the discriminating tubes V,--i together with the filter 20, may be eliminated. The op erating point of the tubes V,V,' will be so set that the signal S, will be suppressed by these tubes, while signals of amplitude 8 and S, will be passed. The amplifier V will transmit all three signals, however, and by properly adjusting its degree of amplification, the components corresponding to S, and S,;"will balance out the corresponding components passed by the discriminating tube, so that signals S, and S, will disappearwhile the signal S, Will be transmitted through the amplifier V to the outgoing line.

This principle may be extended to the selection of any desired current from currents of as many different amplitudes as desired provided tubes having proper operating characteristics are used. it will be readily seen, for example, from Fig. 10 and the as sociated curves that the first discriminating device V ,-V,' can be used to eliminate all amplitudes below the amplitude which it is desired to select. The amplitudes above this limit will then be transmitted to the next discriminating device V,--V,' and its associated amplifierv The discriminating device V,--V may then be adjusted to eliminate in its output circuit the component corresponding to the signal of the desired amplitude, while passing all amplitudes above that which is to be selected. The undesired amplitudes will then be balanced out by means of the components appearing in the output circuit of the amplifier V While the componentcorresponding to the desired amplitude will not be balanced out, owing to the fact that this component is transmitted by the amplifier V but isnot transmitted by the discriminating arrangement V,V,'.

It will be obvious that the general principles herein disclosed may be embodied in many other organizations widely different from those illustrated, Without departing from the spirit of the invention as defined in the following claims.

What is claimed is:

1. The method of discriminating between currents of the same frequency but of different amplitudes, which consists in trans lating said currents without changing the relative amplitudes of the individual currents, translating said currents to produce a change in the relative amplitudes of the individual currents, and combining the resulting components so that components of certain amplitudes neutralize each other.

2. The method of discriminating between currents of the same frequency but of different amplitudes, which consists in trans-- latin said currents without changing the relative amplitudes-t the component currents, translating said currents to produce a change in the relative amplitudes of the component currents while producing such change in the. amplitude 0 the undesired component that it will be'equal in amplitude but opposite in sign to the corresponding component resulting from "said men'tioned translating action, and combining the components resulting from the action of both translating actions.

' 3. Themethod of discriminating between currents of the same frequency but of different amplitudes, which consists in changing the amplitudes of said component currents without disturbing the amplitude. ratio 4 between said component currents, changing the amplitudes of the component currents such a manner as to produce a change in the amplitude ratio between the components,

and combining the resultant components 111- sucha manner as. to'neutralize undesired components.

4. The method of discriminating between currents of the same frequency but of different amplitudes, which consists in changing the amplitudes of saidcomponent currents without changing the amplitude ratio a between theldiflt'erent components, changing ponents to the same amplitude as the corresponding components resulting froin the first mentioned operation, and combining the componentsresulting from" both opera tions in such a manner as to neutralize the undesired components.

5. The method'of discriminating between currents of the same frequenc but-of different amplitudes, which consists in amplitying all said component currents by the currents by different factors, and combining the resultant components in such a manner as to neutralize undesired components;

6. The method of. discriminating between currents ofthe same "frequenc but of'dif ferent amplitudes, which consists in ampli-' fying all said components by the same factor, amplifying the components by different factors so chosen as to produce ourrentsof the same amplitude as regards certain com-ponents as t e corresponding components resultingfrom the first mentioned operation, and combining the components resulting from both operations in such a manner that components of the same ampli tude neutralizev each other.

7. The method of discriminating between currents of different amplitudes, which consists in suppressing all currents having amplitudes'llower than a desired minimum amplitude, translating the remaining components in suclr'manner as to suppress all components having an amplitude greater than an upper limiting amplitude, and transmitting the remaining COIHPOnQlltS,

-. v8.- The method of discriminating between currents of different amplitudes, which consists in suppressing components-having am plltudes below a minimum desired amplitude, amplifying the remaining components without changing the amplitude ratio of such components, amplifying said compo-.'

nents in such -'a manner as to change the amplitude ratio of the components, and combining the com onents resulting from tude, amplifying the remaining components the-last two operat onsso that undesired without changing the amplitude ratio between the components, also amplifying said remaining components 1n such a manner as' to change the amplitude ratio by bringing the" amplitudes of undesired components to the same level as corresponding components resulting from the preceding operations, and combining the components resulting from both operations in such a manner that components havin the same amplitude will v neutralize each ot er.

10.- The method of discriminating between currents; of different amplitudes, which conslsts' in suppressing components having amplitudes lower than a desired minimumamplitude, changing the amplitudes of the remaining components without changing the amplitude ratio between the different, components, changing the amplitudes of said remaining components in such a manner as to change the 'ratio between the amplitudesof the different components, and same factor, amplifylng certain component combining the components resulting from the "last two operations so 'that',undesired components neutralize each other.v

' will be neutralized.

'12. The method of discriminating between currents of difierent amplitudes, which consists in translating the various components to neutralize undesired components.

13!. The method of discriminating between currents of diderent amplitudes, which consists in translating the various components in such manner as to suppress components having amplitudes lower than a desired minimum amplitude, translating the remaining com onents without changing the relative amp itudes of the various components, translating said remainin components to change the relative amp itudes of the various com as to bring un esired components to the same amplitude as that of corresponding components resulting from the preceding operation, and combining the components resulting from both operations in such a manner that components of the same amplitude will be neutralized.

14; A system for discriminating between currents of the same frequency but of different amplitudes, comprising a translating device for changing the amplitudes of said various components without changing their ratio, a second translating device for producin a change in both amplitude and amplitu a ratio of the various components, and means for combining the components resultin from the action of both translating devices in such a manner thatundcsired components will be neutralized.

15. A system for discriminating between currents of the same frequency but of differ- .ent amplitudes, compmsmg means for amplifying said component currents without changing their amplitude ratio, means for ampllfylng certain components to a greater degree than others, and means for combining components resulting from both amplifymg operations in such a manner as to neutralize undersired components.

16. A system for discriminating between currents of the same frequency but of different amplitudes, which comprises. a vacuum tube circuit arrangement adapted to amplify all said components by the same factor, a second vacuum tube circuit arrangement adapted to amplify various components by 'difierent factors, and means. to combine the com onents resulting from the action of both tubes in such a manner as to neutralize undersired components.

17. A system for discriminating between nents in such a mannermenses currents of the same frequency, but of different amplitudes, which comprises a vacuum tube arrangement for amplifying said components by the same factor, a second vacuum tube arrangement for amplifying components of ditferent amplitudes by different factors so chosen that the amplitudes of certain components, when amplified, will be equal to the amplitudes of the corresponding components resulting from the action of the first vacuum tube arrangement, and

means for combining the components resulting from the action of both vacuum tube arrangements in such a manner that components of equal amplitude will neutralize each other.

18 A system for discriminating between currents of different amplitudes, which comprises means for suppressing all components having an amplitude lower than a minlmum desired amplitude, and means for suppressing currents having amplitudes greater than a maximum desired amplitude. 19. A system for discriminating between currents of different frequencies, which comsired minimum amplitude, means for amplifying all the remaining components by the same factor, means for amplifying said remaining components b different factors, and means for combining the components resulting from the last two operations in such a manner that undesired components will be neutralized.

21. A system for discriminating between currents of difi'erent amplitudes, which comprisesmeans for suppressing components having amplitudes below a minimum desired amplitude, means for amplifying all the said remaining components by the same factor, means for amplifying sa1d remaining components by different factors so chosen that certain components, when am plified, will have the same amplitude as corresponding components resulting from the previous operations, and means for combining the components resulting from the last two operations in such a manner that components of equal amplitude will be neutralized.

22. A system for discriminating between menaee currents of difierent amplitudes, which comprises means for suppressing components having amplitudes lower than a minimum desired amplitude, a vacuum tube arrangement for amplifying all of said remaining,

components by the same factor, a secon vacuum tube arrangement for amplifying said remaining components by different factors, and means for combining the components resulting from the action of both vacuum tube arrangements in such a manner as to neutralize undesired components.

23. A-system for discriminating between currents of (lifierent amplitudes, which comprises means for suppressing components having amplitudes below a minimum desired amplitude, a Vacuum tube arrangement for amplifyin the remaining components by the same actor, a second vacuum tube arrangement for amplifying said remaining components by different factors so chosen that certain components, when amplilied, will have the same amplitude as corre-\ sponding components resulting from the actime of the first vacuum tube arrangement, and means for so combining the components resulting from the action. of both vacuum tube arrangements that components having the same amplitude will neutralize each other.

In testimony whereof, I have signed my name tothis specification this 1st day of October, 1921.

RALPH W. DEARDORFF. 

